Using principally the mouse mixed-leukocyte culture reaction as a model system for the generation of cell-mediated immunity, we will investigate mechanisms of the differentiation of T lymphocytes (cortisone-resistant thymocytes) to cytotoxic effector cells. This research will encompass the following objectives. 1. A thorough investigation of the relationship of T cells to the generation of cytotoxicity in MLC. 2. Analysis of T cell surface antigens during generation of cytotoxicity in MLC, with particular emphasis on recognition/binding units. 3. Analysis of the role of macrophages in the development of T cell immunity. 4. Analysis of patterns of protein synthesis in T cells during their sensitization in the mixed leukocyte culture reaction, utilizing double-label radioisotope tagging followed by polyacrylamide gel electrophoresis, immunoelectrophoresis/autoradiography, and iso-electric focusing.